1. Field of the Invention
The present invention relates generally to the field of wireless communication, and more particularly relates to methods and apparatus for frequency synthesis with arbitrarily fine frequency step sizes which are smaller than the frequency step sizes of any of a plurality of adjustable oscillators which are based on phase-locked loops.
2. Background Information
Advances in semiconductor manufacturing processes have resulted in the production of integrated circuits having many millions of transistors as well as other active and passive components. The same advances that have provided the reduction in physical dimensions necessary to integrate millions of electrical elements on a single chip, also provide dramatic increases in operating frequency for these integrated circuits. Integrated circuits implementing logic functions now commonly operate at several GHz, with an order of magnitude increase in operating frequency expected in a few years.
The miniaturization of physical dimensions, coupled with the increase in functionality made possible by such advances in semiconductor technology, have also led to the rapid growth of numerous classes of electronic products, many of which can benefit from the capability of wireless communication. Examples include, but are not limited to, computers, personal digital assistants, cellular telephones, and many others, all which may benefit from wireless access to one or more communication networks. The expression “wireless communication” commonly refers to radio-based communication.
Although superheterodyne architectures have been used in previous generations of radios, implementation of radios in integrated circuits for consumer electronic products can be made more cost-effective through the use of image reject mixers. The Weaver Image Reject Mixer is a known architecture that uses two local oscillators in its implementation.
It is expected that many consumer electronic products having wireless communication capability will need to send and/or receive information over a number of relatively narrow channels within an allocated portion of the electromagnetic spectrum. In order to tune transmitters and/or receivers which use an image reject mixer architecture, such as the Weaver image reject mixer, conventional designs have attempted to adjust the frequency of the local oscillators in small steps.
What is needed are methods and apparatus for achieving a fine resolution frequency step size.